1. Field of the Invention
The present invention relates to a semiconductor memory device, for example, a semiconductor memory device for storing data as a state of majority carriers accumulated in a channel body of a transistor formed in a substrate such as an SOI substrate, and method of manufacturing the same.
2. Description of the Related Art
A semiconductor memory device that can achieve dynamic storage in a simpler cell structure has been proposed recently for the purpose of replacing conventional DRAM (JP 2002/343886A. FIGS. 1–4). A memory cell includes a transistor having a floating body (channel body) formed in an SOI substrate. The memory cell can achieve binary storage as a first data state (for example, data “1”) in which a certain amount of majority carriers are accumulated in the body and a second data state (for example, data “0”) in which a certain amount of majority carriers are released from the body.
Such the memory cell is called a “FBC (floating body cell)” and the semiconductor memory device using the FBC is called a “FBC memory”. The FBC memory is not provided with a capacitor that is employed in a normal DRAM. Therefore, it has a simple cell array structure and a small unit cell area, and accordingly it can be highly integrated easily.
Similar to other conventional semiconductor memory devices such as DRAM, the FBC is also desired for: (1) preventing occurrences of data destruction; (2) down-sizing; (3) reducing parasitic resistances and variations thereof; and (4) elongating a data holding time.